1. Field of the Invention
The present invention relates to surgical instruments for laser cardiac ablation procedures. More particularly, the invention relates to a wand including a fiber optic transmission channel for atrial cardiac ablation.
2. Description of the Prior Art
A. Atrial Fibrillation
It is known that at least some forms of cardiac arrhythmia are caused by electrical impulses traveling through the cardiac muscle tissue by abnormal routes. In a normal, non-arrhythmic heart, electrical nerve impulses travel in an orderly and well-defined fashion through the sinoatrial node and then through the atrioventricular node in order to create an orderly flow of nerve impulses that lead to contraction in the heart.
In cardiac arrhythmia, cardiac impulses travel disorderly and undesirable paths through the cardiac tissue leading to disorderly and inefficient contraction of heart muscle. These fibrillations prevent the heart from pumping blood efficiently and can lead to death.
B. Maze Procedure—Generally
One technique for treating atrial fibrillation is to surgically create lines in the heart muscle tissue (myocardium) whereby electrical conduction of nerve impulses is blocked or rerouted. This technique for creating lines of electrical blockage is referred to as the Maze procedure.
Initial approaches to performing the Maze procedure involved invasive surgery in which a series of linear incisions are made in the cardiac tissue and then sutured together. The lines of scar tissue that form in the incisions do not conduct nerve impulses and are intended to prevent disorderly contraction of the atrial tissue.
In a typical Maze procedure, up to six non-conductive lines are required. Each of the non-conductive lines is typically several centimeters in length. Once these lines scar and heal, they disrupt electrical pathways that may support atrial fibrillation. Examples of the Maze procedure and other surgical techniques for treating atrial fibrillation are described in Chiappini, et al., “Cox/Maze III Operation Versus Radiofrequency Ablation for the Surgical Treatment of Atrial Fibrillation: A Comparison Study”, Ann. Thorac. Surg., No. 77, pp. 87–92 (2004) and Cox, “Atrial fibrillation II: Rationale for surgical treatment”, J. Thoracic and Cardiovascular Surg., Vol. 126, No. 6, pp. 1693–1699 (2003).
C. Less Invasive Maze Procedure Technologies
Less invasive ablation techniques have also been utilized to perform the Maze procedure. In such techniques, the surgeon typically drags an electrode in a linear fashion along the endocardial (internal) or epicardial (external) surface to produce a series of focal lesions. The scaring created by the focal lesions is hopefully contiguous and non-conductive of electrical impulses. For endocardial use, standard ablation catheters or catheters with extended distal electrodes are employed. Epicardially, specially designed handheld probes with a distal electrode for the application of ablating energy are often used.
For the greatest likelihood of success in a Maze procedure, it is particularly important that the lesions created be transmural. A transmural lesion extends through the full wall thickness of the cardiac muscle at the location of the lesion. One factor that obstructs obtaining transmural lesions from an epicardial approach of the heart is the cooling effect of blood in and around the heart. This is a particular difficulty when radio frequency (RF) energy is employed. The application of RF energy relies exclusively on thermal diffusion to create transmural lesions. The cooling effect of blood within the atrium tends to limit the depth to which thermal lesions can be formed.
It is desirable to create a full thickness transmural lesion but undesirable to perforate the atrial wall. Perforation of the atrial wall leads to a weakening of the heart structure as well as significant bleeding during surgery that must be controlled.
Additionally, producing transmural lesions with RF energy tends to heat the surface tissue at the point of probe contact this. This tends to create burns and adhesion between the probe and the heart tissue. Such adhesions can insulate the probe from the heart tissue blocking the efficient application of energy. These procedures are also a problem for the surgeon and staff who often must stop to clean the tip of the probe.
A discussion of techniques and technologies for treating atrial fibrillation is set forth in Viola, et al., “The Technology in Use for the Surgical Ablation of Atrial Fibrillation”, Seminars in Thoracic and Cardiovascular Surgery, Vol. 14, No. 3, pp. 198–205 (2002). Viola et al. describe numerous ablation technologies for treating atrial fibrillation with the Maze procedure. These include cryosurgery, microwave energy, radiofrequency energy, and laser ablation.
D. Laser Ablation and the Maze Procedure